CN112119207A - Compact Rankine turbine generator apparatus for distributed Cogeneration - Google Patents

Abstract

A compact cogeneration plant comprising: a) a heat generating system connected to a steam generator, a condenser and an internal working fluid, wherein the steam is obtained by external combustion of a suitable fuel in a boiler and/or by directing external hot gases to the boiler; b) a generator system, comprising: i) one or more radial and/or axial turbines; ii) an axial flow generator; and iii) an electronically controlled inverter. The fuel may be a solid, liquid or gaseous fuel. Both the turbine and the generator have passive magnetic and electric bearings. The apparatus does not use mechanical seals because all moving parts are contained within the working fluid of the pressure vessel of the working fluid.

Description

Compact Rankine turbine generator apparatus for distributed Cogeneration

Technical Field

The present invention relates to the field of power generation and heat generation equipment. In particular, the invention relates to cogeneration plants or small plants.

Background

Distributed power generation equipment is a low power generation system (less than 1000 kilowatts) that can supplement part of the power consumption of a customer facility (without affecting the grid) or inject power into the grid without requiring modifications thereto.

Cogeneration systems are devices or stationary facilities that utilize the waste heat of power generation equipment to supply, in whole or in part, the heat demand of users. In contrast, there are cogeneration systems that generate electricity using waste heat of a thermodynamic process (furnace, boiler, etc.).

The invention can function in either of two scenarios, i.e. self-heating or heating with external waste heat. In both cases, the electricity generated by the device supplements the consumer's consumption of electricity, partially or totally, and by supplying thermal and electrical energy jointly rather than separately, the overall fuel demand is significantly reduced.

The way to achieve this is based on the implementation of a Rankine (Rankine) type thermal cycle (liquid-vapor), which drives a high-speed microturbine that drives a permanent magnet generator. The electronic inverter supplies power to the local grid (customer facility).

There are many different technical solutions to achieve cogeneration of heat and power. The heat engine may be based on various thermal cycles, such as the brayton (Bryton) cycle, the Otto (Otto) cycle, the Diesel (Diesel) cycle, and the stirling (stirling) cycle. The generator may be synchronized with the grid or may power an electronic inverter. There may be a direct coupling between the heat engine and the generator, or there may be an intermediate fixed or variable reduction gearbox. Even fuel cell based systems exist, in which case the heat engine and the generator are one and the same device.

The cogeneration systems existing in the prior art face the following technical problems that the plant of the present application aims to overcome:

a) machines based on Otto and Diesel cycles (piston engines) are extremely sensitive to the type and quality of the fuel they use. These machines must have well controlled characteristics such as octane number, viscosity, impurity content, humidity, etc. Additionally, their components are subject to significant friction due to the internal mechanisms they use. Therefore, they require complex lubrication systems and regular and rigorous preventive maintenance.

b) Machines (gas turbines) using the Bryton cycle do not require lubrication, either partially or completely, because they consist of a much smaller number of moving parts. Their main problem is sensitivity to fuel quality. When internal combustion is used, the presence of impurities in the fuel can cause severe post-combustion corrosion problems in the most thermally and mechanically demanding components.

c) The Stirling type machine (dual piston system) solves the problem of sensitivity to fuel by using an external combustion chamber. They do not address the lubrication problem when using pistons. The main problem with Stirling machines is that they require large dimensions to produce similar power to previous systems.

US patent publication No. US6234400 relates to a cogeneration plant for buildings and houses, in which the condenser of the heat cycle is an air cooler and/or a hot water storage tank for heating. It uses a radial flow generator externally coupled to a low speed screw-type expander. It does not specify the type of bearing or lubricant used, which seems to be conventional.

U.S. patent publication No. US2006/220388 relates to a combined Bryton/Rankine turbine group in which the turbine and compressor are mounted on the same shaft as the permanent magnets and radial generator. The assembly is housed in the same housing and supported by conventional bearings. The working fluid of the Rankine turbine is isolated from the remaining fluid by conventional mechanical seals.

General electric company offers general electric cleaning cycle equipment (GE clean cycle device) under the license of carentix Technologies. This is an organic Rankine cycle that feeds high speed turbine generator components into a sealed vessel without the need for mechanical seals and lubrication. In this case, the generator is a radial generator. The rotating assembly is supported by active magnetic bearings, which, unlike completely passive systems, require complex control electronics and a constant power supply. In the event of a complete power outage, the active magnetic bearings may expose the shaft to direct mechanical contact with the stator, resulting in severe damage.

Kapton Turbine Corporation (Capstone Turbine Corporation) developed a compact Bryton Turbine generator in which the Turbine-compressor-generator assembly was supported by passive air bearings. In this case, the generator is a radial generator, the air bearing being subject to mechanical wear during opening and closing, based on rheological phenomena that depend on the properties of the gas (generally air). Furthermore, the internal combustion of the Bryton cycle makes it highly sensitive to the type and quality of fuel.

Disclosure of Invention

The present invention is a compact cogeneration plant that uses various types of fuels (gaseous or liquid hydrocarbons, biofuels, solid organics, etc.) as energy sources. The apparatus allows for providing power to an isolated or interconnected low voltage electrical grid while providing heat to an external cooling fluid that can be used as a heating source or heat source for other processes.

The present invention is based on the use of new and less industrially known technologies such as axial and low hysteresis generators, passive magnetic bearings and passive dynamic bearings.

The invention is, in turn, selected from existing and widely spread technologies such as: gas, diesel, pellet burners; shell and tube heat exchangers, plate heat exchangers, concentric tube heat exchangers; radial and axial microturbines; centrifugal and positive displacement pumps; a power electronics device and a microcontroller.

The use of microturbines, generators with low magnetic hysteresis and passive magnetic bearings gives the present invention superior operating characteristics compared to the prior art in terms of high operational reliability and minimum maintenance requirements.

The use of an external fuel burner and heat exchanger gives the present invention versatility over the prior art in terms of acceptable fuel type and quality.

Drawings

FIG. 1 is a schematic diagram of an embodiment of the present invention in which fuel is used as the energy source.

FIG. 2 is a schematic diagram of an alternative embodiment of the present invention in which waste heat from another process is used.

Fig. 3 is a cross-sectional view of the rotating system.

Fig. 4 is a schematic cross-sectional view of an axial flow generator.

Fig. 5 is a schematic cross-sectional view of one end of the shaft 17.

Fig. 6 shows three views of a compact cogeneration plant and compares its dimensions with a common adult form as a reference.

Detailed Description

The present invention is a compact cogeneration plant that uses various fuels (gaseous or liquid hydrocarbons, biofuels, solid organics, etc.) as energy sources. The plant is also capable of generating electricity using waste heat from another independent process as a source of energy.

Fig. 1 shows a fuel burner 13, a high-pressure turbine 01, a low-pressure turbine 02 and a recuperative heat exchanger 07 for cooling fluid.

The hydraulic pump 04 pumps internal working fluid (such as water or some organic fluid) in a high pressure fluid state to one side of the heat exchanger 05. On the other side of the heat exchanger 05, the mixture of hot gases is circulated in a burner 13 of a type suitable for it, burning some gaseous, liquid or solid fuel 12. Fig. 2 shows a variant of this solution, in which the hot exhaust gases of another machine or of a separate treatment process 32 are suitably led 33 to a heat exchanger 05. In this scenario, the fuel is not self-combusting.

Fig. 3 shows a rotating system comprising two turbines 01 and 02, a generator 09, a passive magnetic bearing 14, an electric bearing 15 and a whole turbine group pressure vessel 16.

The working fluid is heated in the heat exchanger 05 and undergoes a phase change until it becomes a dry or slightly humid vapor and is directed to the turbine 01 where the working fluid provides mechanical power at the expense of reducing its pressure and temperature. In an alternative of the invention, the working fluid is led to a second turbine 02, where the working fluid undergoes a second expansion and cooling, providing more mechanical power.

The working fluid at low pressure enters one side of the heat exchanger 03, is cooled in the heat exchanger 03 to undergo complete condensation and is then led back to the hydraulic pump 04, which is always kept in a closed circuit and hydraulically isolated from the rest of the system and from the surroundings.

The cooling fluid 06 circulates through the other side of the heat exchanger 03 and absorbs the heat provided by the working fluid of the plant. This coolant, which is not in direct contact with the working fluid, passes through the heat exchanger 07 to absorb the waste heat of the combustion gases from the burner 13 or the hot gases from the external process, thus increasing its temperature and the overall efficiency of the plant. This higher temperature cooling fluid 08 allows excess heat to be delivered for heating buildings or as a heat source for various industrial processes. In an alternative of the invention, the coolant does not pass through the heat exchanger 07, but is led directly to the cooling tower.

The turbines 01 and 02 rotate in unison with a shaft that also contains permanent magnets and the rotor of an axial flow generator 09. The turbine set rotates at high and variable speeds and allows the generator to provide electrical power in the form of high frequency alternating current. The electronic device 10 adapts the power provided by the generator and injects it into a low voltage grid (e.g., 380 volts) that can be connected to various loads. The low voltage grid may or may not be connected to a larger distribution network.

The turbine group is supported and radially centered by a radial passive magnetic bearing 14. The turbine group may be oriented vertically or horizontally and maintain its axial position by one or more passive dynamic bearings 15 operating above a certain rotational speed. When it rotates at high speed, the turbine group remains mechanically free from contact with the rest of the plant, being supported and stabilized only by passive electromagnetic forces.

The turbine group, the coils of the generator, the passive magnetic bearings 14, the electric bearings 15 and other support systems for starting are completely housed inside a sealed container 16 which keeps the working fluid inside the aforesaid closed circuit.

Fig. 4 shows an axial flow generator 09 comprising two or more rotor disks 18 connected to a shaft 17, each rotor disk containing permanent magnets 19. Between each pair of discs there is placed a stator with windings 22 and a ferromagnetic core 21 with their respective cooling ducts 24. That is, the axial-flow generator 09 is formed of a rotor assembly and a stator assembly. The rotor assembly is fixed to the shaft 17 of the turbine group and has an even number of permanent magnets 19, the permanent magnets 19 being engaged in the non-ferromagnetic discs 18 and opposing each other in an attracting configuration. The generator may comprise two or more discs with magnets. On the outer surface of the disc at each end, a disc 20 of ferromagnetic material, in line with the rotor, closes the magnetic circuit.

The stator assembly houses a conductor 22, the conductor 22 being wound around a number of high resistance ferromagnetic material cores 21. These cores allow the magnetic circuit between each pair of opposing magnets to be closed. The outer periphery of the conductor is in contact with a thermally conductive material 23, and the thermally conductive material 23 dissipates internal heat to the generator housing. Circulation ducts 24 in the heat conductors and ferromagnetic cores allow process gas caused by viscous forces to flow between the rotor and stator. This flow increases heat removal and heat transport in the innermost region of the stator.

Fig. 5 shows the position of a passive magnetic bearing 14 comprising a moving magnet 25 and a stationary magnet 26 as well as shaft stops 28 and auxiliary bearings 29 for start stop. At the same end of the shaft is shown an electric bearing 15, which electric bearing 15 is formed by an assembly of a conductor disc 30 and a stationary permanent magnet 31, coinciding with the shaft. The turbine group is radially supported near the end of its shaft 17 by two passive magnetic bearings 14. Each bearing is formed by one or more pairs of permanent and concentric annular magnets, one of which is a movable magnet 25 and the other is a fixed magnet 26. The latter is located on an axial aligner 27 which allows it to be aligned correctly even in the case of possible length differences between the turbine group and the stator of the assembly. The stabilisation of the axial position of the turbine group is achieved by means of one or more electric bearings comprising a solid or perforated conductor disc 30 fixed to the shaft and two sets of permanent magnets 31 in a repelling arrangement opposite each other supported by a fixed disc. This configuration may be reversed, as shown in fig. 3, where the drive disk is fixed to the housing and the disk supporting the magnets rotates with the shaft.

The novel technical characteristics of the equipment are as follows:

1. it uses a turbine driven by liquid-vapor thermal cycle (Rankine type) and a low-hysteresis axial-flow generator mounted on the same shaft as the power plant. In this way, the generator can be efficiently operated at high speed (high frequency).

Although Rankine cycle power plants have been disclosed, these power plants tend to be large. Some compact generator systems use a Rankine cycle, but they typically incorporate a speed reduction device between the turbine and the generator, which is synchronized with the grid.

2. No lubrication is required for any of its components. The rotating system comprising the turbine and the generator does not require any kind of lubrication, since magnetic and electric bearings are used without mechanical friction. Conventional generators (generators, including large power plants) use lubricating oil on all rotating and friction parts. The bearings of the device are driven by passive electromagnetic forces and do not require monitoring and control electronics as do active magnetic bearings.

3. The heat source and the cold source are completely outside the thermal cycle. Unlike piston engines or gas turbines (Bryton cycle), such systems externally burn fuel similar to boilers. Typically, this method is used for large power plants, but is not suitable for small installations.

With regard to the above technical features, the following advantages can be noted:

1. the number of moving parts is significantly reduced by not using a reduction gear. Because the turbine and generator are contained within the same sealed vessel and are submerged in the working fluid, it does not require mechanical seals. These characteristics improve overall system performance.

2. Very little maintenance is required because there is no need to replace the lubricant or parts that are severely worn by friction. The reliability of the system is high because the passive bearings are simple in design and work even with a complete shutdown of the system until the turbine set is slowed down significantly and can rest on the auxiliary starting bearings.

3. External combustion eliminates the general corrosion and stress corrosion problems associated with combustion products in internal combustion systems. In this way, the requirements on fuel quality (presence of corrosive agents, humidity, etc.) and fuel type (calorific value, flame speed, etc.) are minimized. This allows great flexibility in the type of fuel used, including solid fuels such as biomass. Waste heat from other processes may also be used without the need for additional fuel.

Claims (11)

1. A rankine cycle based compact cogeneration plant comprising a power plant formed by one or more radial and/or axial turbines connected to an axial flow generator, wherein the turbines and the generator are mounted on the same shaft forming a turbogenerator assembly.

2. The compact cogeneration plant of claim 1, wherein the turbine generator assembly is radially supported by a passive magnetic bearing comprising one or more concentrically moving annular magnets and one or more stationary annular magnets, the passive magnetic bearing being mounted near an end of said shaft.

3. The compact cogeneration plant of claim 2, wherein the passive magnetic bearing has an axial aligner to absorb length differences between the stator and rotor to ensure their correct alignment.

4. The compact cogeneration apparatus of claim 2, wherein the turbine engine assembly is axially supported and stabilized by one or more passive dynamic bearings and conventional auxiliary bearings for start-stop.

5. The compact cogeneration plant of claim 4, wherein the passive electrically powered bearing comprises a solid or perforated conductor disc and a set of permanent magnets opposing in a repelling arrangement.

6. The compact combined heat and power plant of claim 5, wherein one of the conductor disc and the set of permanent magnets is fixed to a housing, and the other of the conductor disc and the set of permanent magnets is connected to the shaft.

7. The compact cogeneration plant of claim 1, wherein the fuel comprises a solid, liquid, or gaseous fuel.

8. The compact cogeneration apparatus of claim 4, wherein said turbine generator assembly and said passive magnetic bearing and said passive dynamic bearing are housed together in a sealed container containing working fluid pressure and no mechanical seals.

9. The compact cogeneration plant of claim 8, wherein the generator comprises an internal cooling duct through which the working fluid flows between the rotor and the stator under viscous drive.

10. The compact cogeneration plant of claim 1, wherein the generator has a low hysteresis and high resistance core.

11. The compact cogeneration plant of claim 1, wherein the heat source and the heat sink are external to the thermal cycle, whereby the fuel is externally combusted and the coolant does not contact the working fluid.

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